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NACA RB No. LlO

5

Stress-strain tests of the material were made withsingle-thickness specimens in a roller-tpe compressionfixture similar to that shown in figure of reference 2.Copres-ive stress-strain curves are shown in figure 2.The values o' the convopessive yield stress, determinedby the C.2-percent--offset method, and of the modulus ofelasticity are givcn in table 2.METHOD OF TESTINGThe colurnn tests were made in a 300,OO0-pound-capacity compression testing machine that is accuratewithin three-quarters of 1 percent for the rarrnge of loadused in the tests.A Z-sectibn column under test is shown in figure 3.The displacement of pointers, supported by extensicnarms attached to the flanges of the colun.ns, was measuredby the optical micrometers that can be seen in figure 3.The critical compressive stress was obtained from stress-distortion curves in the manner described. and illustratedin reference 3. In this method, the critical stress isdetermined as the point near the top of the knee of thestress-distortion curve where a marked increase in distor-tion first occurs with small increase in stress.RESULTS AND DISCUSSIONThe variation of o and 0max with L/b , foreach of the different types of column tested is presentedin figure . Columns having - 2L and b 0.5t Swdeveloped bending failure for - > 7. A definite risein critical and maximum stresses when the columns becomevery short is shown by these curves. For all except thevery short columns, however, the curves are relativelylevel. The number of half-waves of the buckling patternthat occurred in each case is also indicated in figure 4.It ]has been found desirable for test purposes tomake the column length such that an odd number of half-waves.develops, because of the convenience in measuring